1. Field of the Invention
The present invention relates to a power supply device for a light emission display device, and more particularly, it relates to a power supply device having a stabilizing circuit for standard voltage to stably provide a data voltage to an integral circuit of a data driver of the light emission display device.
2. Description of the Related Art
In general, an organic electroluminescent (referred to as “EL” hereinafter) display device classifies phosphorus organic components into pixels arranged in a matrix format, and visualizes an image by controlling the amount of current flowing to the phosphorus organic components. Such an organic EL display device is an advanced display which is highly responsive, consumes low power, and has a large view angle. Thus, the organic EL display is expected to be the next-generation display.
FIG. 1 illustrates a light emission mechanism of an organic EL display (hereinafter, alternatively referred to as OLED).
In general, an OLED device electrically excites phosphorus organic components, and visualizes an image by voltage-programming or current-programming M×N numbers of organic light emitting cells. As shown in FIG. 1, these organic light emitting cells include an indium tin oxide (ITO) pixel electrode, an organic thin film, and a metal layer. As shown in FIG. 1, the organic thin film has a multi-layered structure including an emission layer (EML), an electro transport layer (ELT), and a hole transport layer (HTL) so as to balance electrons and holes and thereby enhance efficiency of light emission. Further, the organic thin film separately includes an electron injection layer (EIL) and a hole injection layer (HIL).
Methods of driving the organic light emitting cells having the foregoing configuration include a passive matrix method and an active matrix method. The active matrix method employs a thin film transistor (TFT). In the passive matrix method, an anode and a cathode are formed crossing each other and a line is selected to drive the organic light emitting cells. However, in the active matrix method, each indium tin oxide (ITO) pixel electrode is coupled to the TFT, and the light emitting cell is driven in accordance with a voltage maintained by capacitance of a capacitor coupled to a gate of the TFT.
FIG. 2 illustrates a pixel circuit of a typical OLED. The pixel circuit includes an OLED, a driving transistor DM, a switching transistor SM, and a capacitor Cst. The driving transistor DM and switching transistor SM may each be provided as a PMOS transistor.
A source of the driving transistor DM is coupled to a power voltage VDD, and the capacitor Cst is coupled between a gate and a source of the driving transistor DM. The capacitor Cst maintains a gate-source voltage at the driving transistor for a predetermined period of time, and the switching transistor SM transmits a data voltage from a data line Dm to the driving transistor DM in response to a selection signal from a current scan line Sn.
A cathode of the OELD is coupled to a reference voltage Vss, and the OLED emits light corresponding to a current applied thereto through the driving transistor DM. Herein, the reference voltage Vss coupled to the cathode of the OLED is lower than the power voltage VDD, and accordingly a ground voltage may be applied thereto.
The data voltage of an OLED display is generated by a direct-current/direct-current (DC/DC) converter (typically employing a charge-pump method) provided in an integral circuit IC of the data driver using external power. The data voltage affects brightness and contrast of a display panel. However, the data voltage may be increased or decreased when there is a sudden drop in the external power or an occurrence of noise, and instability of the data voltage affects the brightness and the contrast of the panel.